解下列一元二次方程1.2x²-8x=02.x²-3x-4=03.2x²+7x-4=0
4.⅔x²=2-⅓x 5.x²+6x-112=0 6.(x-⅔)²=25分之9 7.25x²-10x+1=9 8.x²+2x-99=0= 9.x²+10x+9=0
1. 2x²-8x=0
2x(x-4)=0
2x=0 或 x-4=0
x1=0 x2=4
2. x²-3x-4=0
(x+1)(x-4)=0
x+1=0 或 x-4=0
x1=-1 x2=4
3. 2x²+7x-4=0
(x+4)(2x-1)=0
x+4=0 或 2x-1=0
x1=-4 x2=1/2
4. ⅔x²=2-⅓x
上式两边同乘以3,得 2x²=6-x
移项,得 2x²+x-6=0
(x+2)(2x-3)=0
x+2=0 或 2x-3=0
x1=-2 x2=3/2
5. x²+6x-112=0
(x-8)(x+14)=0
x-8=0 或 x+14=0
x1=8 x2=-14
6. (x-⅔)²=9/25
(x-⅔)²=(3/5)²
x-2/3=±3/5
x=2/3±3/5
x1=2/3+3/5=19/15
x2=2/3-3/5=1/15
7. 25x²-10x+1=9
(5x)²-2×1×5x+1²=3²
(5x-1)²=3²
5x-1=±3
由 5x-1=3 得 x1=4/5
由 5x-1=-3 得 x2=-2/5
8. x²+2x-99=0
(x-9)(x+11)=0
x-9=0 或 x+11=0
x1=9 x2=-11
9. x²+10x+9=0
(x+1)(x+9)=0
x+1=0 或 x+9=0
x1=-1 x2=-9